In concrete slab construction, concrete slabs are cast in place on an underlying support structure. The concrete slabs, particularly in outdoor environments, are subject to thermal expansion and contraction which causes random cracks to form in the concrete. Cracks may also form as a result of movement of the underlying support structure, such as by settling. It is well known, that cracking can be minimized by use of control joints which divide the concrete slab into a number of separate sections.
One method of forming a control joint comprises using a saw to cut a joint into the concrete slab once the concrete has had sufficient time to set. A major drawback with the saw cutting method is that it increases labor costs since the workmen must return to the site to cut the joints a day after the concrete has been poured.
Another method of forming a control joint comprises placing metal or concrete joints on the underlying support structure before pouring the concrete slab. The concrete is then poured in place on both sides of the joint so that the top of the slab is even with the top of the metal or concrete joint. However, most joints do not provide a screeding surface which is helpful in obtaining a flat, level slab of uniform thickness. Those joints which do provide a screeding surface are generally made of concrete. Such joints are extremely heavy and are difficult to transport and handle.